text: Some radioactive fission products can be converted into shorter-lived radioisotopes by transmutation. Transmutation of all fission products with half-life greater than one year is studied in Grenoble, with varying results.
  Strontium-90 and caesium-137, with half-lives of about 30 years, are the largest radiation (including heat) emitters in used nuclear fuel on a scale of decades to ~305 years (tin-121m is insignificant because of the low yield), and are not easily transmuted because they have low neutron absorption cross sections. Instead, they should simply be stored until they decay. Given that this length of storage is necessary, the fission products with shorter half-lives can also be stored until they decay.
  The next longer-lived fission product is samarium-151, which has a half-life of 90 years, and is such a good neutron absorber that most of it is transmuted while the nuclear fuel is still being used; however, effectively transmuting the remaining  in nuclear waste would require separation from other isotopes of samarium. Given the smaller quantities and its low-energy radioactivity,  is less dangerous than  and  and can also be left to decay for ~970 years.
  Finally, there are seven long-lived fission products. They have much longer half-lives in the range 211,000 years to 15.7 million years. Two of them, technetium-99 and iodine-129, are mobile enough in the environment to be potential dangers, are free (Technetium has no known stable isotopes) or mostly free of mixture with stable isotopes of the same element, and have neutron cross sections that are small but adequate to support transmutation.
  Additionally,  can substitute for uranium-238 in supplying Doppler broadening for negative feedback for reactor stability.
  Most studies of proposed transmutation schemes have assumed , , and transuranium elements as the targets for transmutation, with other fission products, activation products, and possibly reprocessed uranium remaining as waste. Technetium-99 is also produced as a waste product in nuclear medicine from Technetium-99m, a nuclear isomer that decays to its ground state which has no further use. Due to the decay product of  (the result of  capturing a neutron) decaying with a relatively short half life to a stable isotope of ruthenium, a precious metal, there might also be some economic incentive to transmutation, if costs can be brought low enough.
  Of the remaining five long-lived fission products, selenium-79, tin-126 and palladium-107 are produced only in small quantities (at least in today's thermal neutron, -burning light water reactors) and the last two should be relatively inert. The other two, zirconium-93 and caesium-135, are produced in larger quantities, but also not highly mobile in the environment. They are also mixed with larger quantities of other isotopes of the same element. Zirconium is used as cladding in fuel rods due to being virtually "transparent" to neutrons, but a small amount of  is produced by neutron absorption from the regular zircalloy without much ill effect. Whether  could be reused for new cladding material has not been subject of much study thus far.